SPECIAL MORPHOLOGY AND TAXONOMY OF SPOROZOA 451 



on the host but the tissue parasites are more disastrous, Myxobolus 

 pfeifferi, for example, causing costly epidemics amongst food fishes, 

 particularly in the barbel (Barbits barbvs L.) of Europe. 



The free or coelozoic forms are the most generalized in structiu'e 

 and the tissue parasites are generally regarded as having been 

 derived from them by adaptation (Auerbach, 1910; Doflein, 1916; 

 Davis, 1917, et ah). They are somewhat more numerous than the 

 tissue-dwelling forms. Kudo enumerating 125 species of the former 

 and 114 of the latter while 3 species are apparently transitional, and 

 7 of unknown habitat. The free forms often show a remarkable 

 resemblance to amoebae; ectoplasm and endoplasm are usually 

 differentiated, the former as in some amoebse, forming a continuous 

 cortical zone about the organism, or as in other t\T3es of amoebse, 

 evident in certain regions only (Fig. 188). It is occasionally pro- 

 vided with bristle-like processes and the pseudopodia of different 

 types are invariably derived from it (Davis) . 



The endoplasm is more fluid than the ectoplasm, contains many 

 nuclei and metaplasmic bodies in the form of fat globules, pigment 

 granules, and crystalline bodies, in some cases embedded in struc- 

 tures which under the name of spherules (Davis) are sometimes so 

 abundant as to give a characteristic appearance to the organism 

 (Fig. 189). 



Like other Sporozoa, the Myxosporidia are highly prolific and 

 adaptations to this end are well marked. Asexual reproduction 

 occurs by simple division or by multiple division (plasmotomy), 

 and by budding. Exogenous budding described by Cohn, 1896 in 

 Myxidiinn UeberJdlhni is regarded by Davis (1916) as abnormal and 

 without significance in reproduction but internal or endogenous 

 budding occurs in SinuoUnea dimorpha, Da\'is, where free cells are 

 formed about nuclei in the endoplasm. These cells, called "gem- 

 mules" by Davis escape from the parent organism and develop into 

 individuals (Fig. 188). 



Propagative reproduction invohes the formation of spores and 

 the nearest approach to sexual processes to be found in the Xeo- 

 sporidia. The process has been described by various observers and 

 the general agreement of these descriptions indicates a common 

 plan throughout the group. Schroder's account of sporulation in 

 Sphoeromyxa sabra~esi. Lav. and Mes. may be selected as an example 

 for the entire Order. This form is parasitic in the sea-horse Siphon- 

 ostoma rondeletii, and like many others has dimorphic nuclei dis- 

 tinguishable by size and structure. Small areas become differen- 

 tiated within the endoplasm and contain two nuclei, one of each 

 type. These areas, the so-called pansporoblasts, are the mother 

 cells of the spores. Each nucleus divides in such order that 7 

 nuclei arise from each; the mother cell then divides into two cells 

 which are destined to form two spores. Each of these cells has 



